The invention relates to a device for the removal of particles and/or screenings from a liquid running in a laundry. An upwardly-inclined screen with penetration gaps or openings in the shape of a cylinder jacket reaches into the laundry, and is partly immersed in the liquid. A parallel conveying track for the material is located away from the screen, in the form of a screw conveyor device, with a housing, a shaft and a conveyor helix which moves alongside the screen and thus picks up the material and transports it upwards.
Such a device may be used for different particles and/or screenings, for example, in the area of sewage technology, and also for filtering plastics residues out of liquids. The description herein always refers to the separation of mostly solid particles and/or screenings and a liquid.
A device of the type described above is known from DE-PS 37 16 434. This device consists of a screw conveyor with housing, shaft and conveyor helix forming a conveying track. The shaft with the conveyor helix is driven by a motor. In its lower section which is immersed in water, the housing of the screw conveyor is substituted at least partly by the screen. The screen consists of screen bars extended throughout a total screen height located in axial direction; that is, parallel to the axis of the shaft of the screw conveyor, and running alongside a cylindrical circumference. In this way, openings through which the liquid can pass, but particles starting from certain dimensions may not pass, are formed in between the grate bars and parallel to the axis of the screw conveyor. The conveyor helix passes alongside the openings of the screen and picks up the particles in the conveying direction. The screen bar sections are triangular or trapezoid in shape with rounded-off edges. The locations of these sections are such that a triangular or trapezoid side of the section points tangentially to the rotating direction of the conveyor helix, causing a narrowest point of the opening on a smallest possible radius to be connected to a proportionally widening, free section of the opening in the flow direction of the liquid. The screen bars forming the opening are interconnected at the outside by supporting bars. The openings are of a relatively great length in the axial direction and extend over almost t he entire screen, even though they are held in place at the outside at certain intervals by supporting bars. If such devices are used in sewage technology, it is unavoidable that the device be not only coated by the real particles but coated in the laundry also, by stones and especially stone chips, as used for putting on icy winter roads, which get into the range of the conveyor helix and of the opening. These stone chips have sharp edges, which put the device under strain in several ways. The stone chips act notably aggressive, thus causing great wear and tear on the screen material. This is accompanied by a deformation of the continuous screen bars, because the stone chips get stuck in the opening gap between the conveyor helix and the screen bars, giving rise to considerable forces exerted by the conveyor helix on the screen bars. The opening is thereby formed by way of the pinched stone, leading to a shattering of the stones. This is not the function of a device for the removal of particles from a laundry, but which could still be tolerated. However, it is much less desirable that the screen bars be bent under this excessive application of forces, i.e., in tangential direction. With this, the opening width is altered and eventually the screen bars are separated from the supporting bars, torn up, and then grazed by the conveyor helix. It has been observed in a device of the type described at the outset that a screen installed in a sewage treatment plant, that was clogged with stone chips was totally destroyed in two days of operation. Another disadvantage of the device with such a screen is insufficient self-cleaning. Through the lateral application of forces between conveyor helix and particles that occurs inclined to the lengthwise direction of the opening, there exists a tendency that the particles are again and again pressed into the opening. Thus, the openings get more clogged so that the liquid may not pass through them. An increase of the liquid level signals the adverse effect.